1. Field of Invention
The invention relates to a pressure-operated mechanism for driving a driven portion or controlling a controlled portion, according to a change in pressure in a pressure chamber, and relates to a water pump including the pressure-operated mechanism.
2. Description of Related Art
In an internal combustion engine, a water pump for circulating cooling water through the water jacket is used. In the water pump described in Japanese Utility Model Application Publication No. 5-58832 (JP-U-5-58832), for example, rotation of an impeller fixed to a rotary shaft causes circulation of cooling water. In the water pump, the driving force generated by the internal combustion engine is transmitted to the rotary shaft via a pulley, which rotates in synchronization with the internal combustion engine, and via a fluid coupling, thereby rotating the impeller. The water pump is configured so that the degree to which the rotary shaft and the fluid coupling are engaged becomes greater as temperature of the cooling water in the water jacket becomes higher. Thus, in the water pump, the higher the temperature of the cooling water in the water jacket is, the higher the rotational speed of the impeller is.
In recent years, as water pumps, of which the driving force transmitted to the rotor of the pump can be changed, those shown in FIGS. 5 and 6, for example, have been studied. As shown in FIG. 5, the water pump 100 includes: a circulation system 20 for circulating the cooling water; and a driving system 30 for driving a rotary cylinder 21 of the circulation system 20. A separation wall 40 for preventing cooling water from leaking from the circulation system 20 into the driving system 30 is provided between the circulation system 20 and the driving system 30.
A flow path 23 through which cooling water flows is formed in a cylinder block 22 of the internal combustion engine. A supporting shaft 25, one end of which is fixed to the separation wall 40, is provided in the flow path 23. At both ends of the supporting shaft 25, bearings 24a and 24b are provided, respectively. The supporting shaft 25 is inserted through the rotary cylinder 21, which is provided with vanes 26, whereby the rotary cylinder 21 is supported rotatably with respect to the supporting shaft 25. An end portion of the rotary cylinder 21 on the separation wall 40 side is fitted with an inductor ring 27 including an iron core.
The driving system 30 includes a housing 31, and a pulley 32 is fixed to the housing 31, the pulley 32 being connected to a crankshaft (not shown) of the internal combustion engine through a belt 33 so that the pulley 32 is driven through the crankshaft. In the housing 31, a slider 34 is provided, at least part of which is engaged with the housing 31 in a splined manner, the slider 34 being able to move to and fro in the axial direction of the rotary cylinder 21 in the housing 31. A magnet 35, which is made of neodymium, for example, is fitted onto an end portion of the slider 34 on the circulation system 20 side so that the magnet 35 surrounds the inductor ring 27 fitted onto the rotary cylinder 21. Each of the inductor ring 27 and the magnet 35 functions as a magnetic portion.
The slider 34 is always urged toward the circulation system 20 side by a spring 36 provided in the housing 31. The torque transmitted from the crankshaft to the housing 31 via the belt 33 and the pulley 32 is transmitted to the rotary cylinder 21 by means of the magnetic interaction that occurs between the inductor ring 27 and the magnet 35, whereby the rotary cylinder 21 is rotated. When the vanes 26 fixed to the rotary cylinder 21 rotates due to this rotation, the cooling water in the flow path 23 is pressure-fed to the water jacket (not shown) of the internal combustion engine.
The inside of the housing 31 is divided into an atmospheric chamber 31a and a pressure chamber 31b by the slider 34. A seal member 37 for sealing between the slider 34 and the inner surface of the housing 31 is provided on the outer surface of the slider 34, and the seal member 37 keeps the pressure chamber 31b airtight. When the pressure in the pressure chamber 31b varies, the slider 34 moves to and fro in the housing 31, whereby the amount of torque that is transmitted to the rotary cylinder 21 via the magnet 35 and the inductor ring 27 is changed. Thus, in the water pump 100, the rotary cylinder 21 is a rotary body that serves as the driven portion driven by the to-and-fro movement of the slider 34; the housing 31 and the slider 34 constitute the operation portion that drives the rotary cylinder 21 according to the change in pressure in the pressure chamber 31b; and the driving system 30 is the pressure-operated mechanism.
In the driving system 30, a pressure pipe 41 is inserted into the pressure chamber 31b of the housing 31. The pressure pipe 41 is supported by a bearing 42 provided in the housing 31 and fixed to another member (not shown), and the housing 31 is rotatable with respect to the pressure pipe 41. A seal 43 for preventing air from leaking out of the pressure chamber 31b is provided between the pressure pipe 41 and the inner surface of the housing 31. A pressure introducing pipe 52 is connected to the pressure pipe 41, and a vacuum switching valve (hereinafter referred to as the “VSV”) 55, which serves as the switching portion, is provided on the pressure introducing pipe 52. The pressure introducing pipe 52 is branched via the VSV 55 at the end opposite to the end at which the pressure introducing pipe 52 is connected to the pressure pipe 41. One branch of the pressure introducing pipe 52 is connected to an intake air passage 57 on the downstream side of a throttle valve 62, and the other branch of the pressure introducing pipe 52 is connected to an atmospheric air introducing portion 54 into which atmospheric air is introduced, in the engine compartment. In the intake air passage 57, the portion downstream of the throttle valve 62 is a negative pressure area in which pressure is lower than the atmospheric pressure when the internal combustion engine is in operation. Specifically, the pressure pipe 41 and the pressure introducing pipe 52 constitute a pressure path 70, and the atmospheric air introducing portion 54 and the intake air passage 57 give a first pressure area and a second pressure area, respectively. Drive control of the VSV 55 is performed by an electronic controller 90, whereby the valve element position of the VSV 55 is changed, which causes the pressure chamber 31b to communicate with the intake air passage 57 or the atmospheric air introducing portion 54 selectively.
Specifically, when the signal for controlling the VSV 55, supplied from the electronic controller 90, is “OFF,” the pressure chamber 31b communicates with the atmospheric air introducing portion 54, and the atmospheric air is introduced into the pressure chamber 31b, whereby the difference in pressure between the atmospheric chamber 31a and the pressure chamber 31b vanishes. Thus, as shown in FIG. 5, the slider 34 is urged by the urging force of the spring 36, and is displaced toward the circulation system 20. When this occurs, the magnet 35 provided on the slider 34 and the inductor ring 27 provided on the rotary cylinder 21 come close to each other in a facing relation, and therefore, the magnetic flux passing through the magnet 35 and the inductor ring 27 increases, and the torque transmitted from the slider 34 to the rotary cylinder 21 becomes relatively large. Thus, the amount of cooling water that is delivered or supplied to the water jacket due to the rotation of the vanes 26 of the rotary cylinder 21 also increases.
On the other hand, when the signal for controlling the VSV 55, supplied from the electronic controller 90, is “ON,” the pressure chamber 31b communicates with the intake air passage 57, and the negative pressure of the intake air is introduced to the pressure chamber 31b, so that the difference in pressure between the pressure chamber 31b and the atmospheric chamber 31a causes the slider 34 to be displaced toward the pressure pipe 41 despite the urging force exerted by the spring 36, as shown in FIG. 6. Thus, the magnet 35 provided on the slider 34 and the inductor ring 27 provided on the rotary cylinder 21 come away from each other in the axial direction of the rotary cylinder 21, which causes the magnetic flux passing through the magnet 35 and the inductor ring 27 to be reduced as compared to the state shown in FIG. 5. Accordingly, the flow rate of the cooling water that is delivered or supplied to the water jacket is reduced.
In this way, in the water pump 100, the flow rate of the cooling water delivered or supplied to the water jacket is appropriately controlled by changing the valve element position of the VSV 55.
In the meantime, there is a water pump 100 in which the pressure introducing pipe 52 is detachable for the purpose of improving the ease of maintenance. Specifically, as shown in FIGS. 5 and 6, it is conceivable that the pressure introducing pipe 52 includes: a first connection pipe 58 that is attachable and detachable to and from the pressure pipe 41 and the VSV 55; and a second connection pipe 59 that is attachable and detachable to and from the VSV 55 and the intake air passage 57. In this case, when a mechanic removes the connection pipes 58 and 59 and leaves them as they are at the time of maintenance or inspection of a vehicle, for example, a problem can occur that it is impossible to cause an appropriate change in pressure in the pressure chamber 31b by switching the VSV 55.
Specifically, when the first connection pipe 58 is disconnected from the pressure pipe 41 or the VSV 55, and the second connection pipe 59 is disconnected from the VSV 55 or the intake air passage 57, the atmospheric air is always introduced into the pressure chamber 31b, and the pressure chamber 31b is maintained at the atmospheric pressure, so that the water pump 100 is always maintained in the state shown in FIG. 5. Thus, it is impossible to adjust the amount of cooling water delivered or supplied to the water jacket by means of the water pump 100.
A water pump 100 is available in which a detection section for, when the first and second connection pipes 58 and 59 are disconnected, detecting the disconnection using the fact that the conditions of flow in the pressure introducing pipe 52 change at the time of the disconnection.
The detection of the disconnection by the detection section is performed as follows, for example. Typically, in an internal combustion engine, the amount of air introduced into the combustion chamber is detected by an air flow meter 60 provided in the intake air passage 57, and the amount of fuel injected into the combustion chamber(s) is derived based on the amount of air detected by the air flow meter 60 in order to set the weight ratio between air and fuel in the combustion chamber to the desired air-fuel ratio. However, when the second connection pipe 59 is disconnected from the VSV 55, for example, air is introduced into the intake air passage 57 through the second connection pipe 59, and therefore, the amount of air introduced into the combustion chamber becomes greater than the amount of air that is detected by the air flow meter 60. For this reason, even when the amount of fuel injection is controlled based on the amount of air detected by the air flow meter 60 so that the air-fuel ratio in the combustion chamber becomes the desired air-fuel ratio, the actual air-fuel ratio becomes greater (leaner) than the desired air-fuel ratio. Thus, it is possible to detect the disconnection of the connection pipes 58 and 59 of the pressure introducing pipe 52 under such conditions. Also when the second connection pipe 59 is disconnected from the intake air passage 57, or when the first connection pipe 58 is disconnected from the VSV 55 or the pressure pipe 41, the disconnection of the connection pipe 58 or 59 can be detected similarly. Specifically, when the connection pipe 58 or 59 of the pressure introducing pipe 52 is disconnected, this abnormality, or disconnection, can be detected based on a change in the conditions of flow in the pressure introducing pipe 52, such as the event that air is introduced from the disconnection point into the intake air passage 57.
When it is determined whether the connection pipe 58 or 59 of the pressure introducing pipe 52 is disconnected, if the cross section of the passage of the pressure introducing pipe 52 is small, the amount of air introduced into the intake air passage 57 when the connection pipe 58 or 59 is disconnected is not so large. Thus, in view of detecting the disconnection, the larger the cross section of the passage of the pressure introducing pipe 52, the better. However, when the cross section of the passage of the pressure introducing pipe 52 is large, the speed at which the slider 34 moves to and fro when the pressure in the pressure chamber 31b rapidly changes at the time of switching the VSV 55 is high, which can cause degradation of durability of the components constituting the driving system 30, degradation of controllability of the internal combustion engine due to rapid change in the speed of rotation of the vanes 26, and increase in the sound of flow in the flow path 23.
The pulsation due to rapid change in pressure in the pressure chamber is a problem that can occur in a pressure-operated mechanism, other than the water pump, in which mechanism a driven portion is driven or a controlled portion is controlled according to a change in pressure in the pressure chamber. Specifically, when, in a pressure-operated mechanism, the pressure path includes the connection passage that is attachable and detachable to and from the pressure chamber, and the cross section of the passage of the pressure path has a size such that it is possible to detect disconnection, driving of the driven portion or control of the controlled portion is abruptly performed due to a rapid change in pressure in the pressure chamber, which can cause pulsation.